Abstract: In order to analyze the increasing accumulative plastic damage of ship stiffened plates, this pa-per combines the interaction coefficients of stiffeners and plates, and with plastic strain of damage evolu-tion being the control parameter, the low-cycle fatigue accumulative increasing plastic damage model and low-cycle fatigue life model for stiffened plates have been derived based on the theory of damage mechan-ics. The fatigue damage variable of the stiffened plate under cyclic loading is then introduced into the accu-mulative plastic strain equation. Next, by means of integral transformation, the evolution equation of axial accumulative plastic strain and the constitutive model for low-cycle fatigue life are deduced under low cy-clic loading. The general high strength steel 402 is adopted, with its related material fatigue characteristic parameters introduced to be compared with the low-cycle fatigue life model of stiffened plates. The theoreti-cal evolution results from the presented models of the accumulative plastic strain damage are compared with finite element modeling results, and the influences of mean stress and rib stiffness ratio on the accumu-lated plastic strain are discussed. The results indicate that the established model well reflects the evolution-al law of the axial plastic strain of the stiffened plate under cyclic loading and brings convenience into the evaluation of low-cycle fatigue strength of ship structures.